My final PDC project has a fair amount of rainwater collection and management inherent to it in that my site is increasingly confronted with period of plenty and then a long dry season at the end of Summer. I have a small slope I can work with, and rainwater collection surfaces.
As part of my assessment for what was possible and how difficult actual construction would be, I've looked into the rain gardens portion of the project from sort of a dual approach.
First, I sought to understand best practices, what plants are appropriate for my climate and designs, and what an actual construction project itself entails. I've taken a number of rain garden classes, but eventually I came across Washtenaw County (Michigan's) Master Rain Gardner certification class (online). This is the same program Franklin County (Ohio, where my PDC site is) Soil and Water Conservation District teaches. I completed the coursework last Winter and submitted a large rain garden design, but had not been able to do the actual hands on installation yet.
Secondly, I've been visiting various existing rain gardens here in the region, particularly older rain gardens to get a sense of how they function and what they come to look like. I wrote one such visit up here in the forums earlier- PDC field trip: Adena Brook rain garden.
Since Autumn (here in the Northern hemisphere) is an excellent time to plant perennials, I decided that even if I couldn't get to installing the larger design right now, I could at least get a small rain garden in and work towards finishing the master rain gardener certification this year, as a means of gaining some of that hands on understanding towards my PDC final design.
I've been in Maryland this early Autumn, not in Ohio (which is the site I'm using for my PDC) so I went ahead and did a small installation to slow, spread, and sink water coming off the hardscape driveway in Maryland as sort of a hands on practice.
My partner and I spent last weekend digging out a 5'x 8' or 40 sq. ft. (or 3.7 sq. meter) small rain garden, digging in a mix of soil and compost, adding a compost layer, building a berm and outflow/overflow pipe and topping the garden with shredded and chipped wood mulch.
Howard County (in Maryland) does an Autumn free tree give away as part of the county's forestry programs in an effort to increase the county tree canopy, so I selected a River Birch this year for the new little rain garden. As part of building it, we did the tree planting as well.
One of our local native nurseries nearby is open well into November and knows their native rain garden plants well, since they construct them too. I'll be selecting some end of season perennials to root in overwinter soon. My design for this Autumn will adapt towards what's available, while next Spring, I'll likely add more plant material. I will likely add some gravel along the outflow to direct and slow that overflow as well.
The site is well over 60' (or 18 meters) from the house, on a gentle downslope (less than a 12% grade,) and in partial sun. The soil is sandy loam with some clay. It infiltrates in under 18 hours. It's built along a pre-existing water path where erosion was occurring before water flows down a steeper hillside path. Part of this construction was an effort to keep water higher on the landscape longer, while supporting wildlife.
Eventually, this may come to be the first of a series of rain gardens, several small and the initially designed larger one, being used to manage water as it moves across the site.
Some of the things I learned from the process: First, check with utilities for areas to avoid. Yes, it's a LOT of work, but a small rain garden like this CAN be dug and filled in a weekend by the two of us (who are both over 50!) That slight bit of clay is actually really useful in building the berm to ensure good water retention. Perhaps most importantly, observing and understanding pre-existing water paths will help get it right. That said, for a next rain garden, or a larger one, I might work with Howard EcoWorks (a local non-profit) and their Seeds of Change nursery.
When the time comes to build out the rain garden system at my Ohio site, renting a backhoe trencher, or perhaps working with a local water harvesting professional for a large scale project like this would be preferable (which is what I had assumed from the outset.)
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Using white flags to mark the edges of the hole and where the berm goes.
Horseshoe shaped rain garden with outflow pipe at the far end
River Birch planted and compost layers in.
All wood mulched in, ready for planting native perennials.
